Positive electrode active material, method for producing the same, and method for using the same

Abstract

A positive electrode active material and a method for producing the same, a positive electrode including the positive electrode active material, a secondary battery including the positive electrode, and an electrical device including the secondary battery. The positive electrode active material has the general formula A3V 2-x M x (P 1-y E y O4)3, wherein A represents an alkali metal element, M represents a doping element substituting for V, M comprises one or more of a transition metal element and a rare earth element, E represents a doping element substituting for P, E comprises one or more of As, Sb, and Bi, 0≦x≦1, 0

Description

[Technical Field]

[0001] Cross-reference of related applications This disclosure claims priority to Chinese Patent Application No. 202210957755.5, “POSITIVE ELECTRODE ACTIVE MATERIAL, AND PREPARATION METHOD THEREFOR AND USE THEREOF,” filed on 10 August 2022, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to the technology of batteries, and more particularly to positive electrode active materials, methods for manufacturing the same, and methods for using the same. [Background technology]

[0003] The cathode material for batteries is a crucial component and significantly impacts battery performance. For example, among the numerous cathode materials for sodium-ion batteries, sodium superionic conductor cathode materials, being polyanionic materials, have become a focus of research in recent years due to their potential advantages such as a stable crystal structure, adjustable operating voltage, and high theoretical specific capacity. However, such materials have several drawbacks, including low electronic conductivity, difficulty in diffusing active ions, and a low charge-discharge voltage plateau, which severely limit their large-scale application in sodium batteries. [Overview of the project] [Problems that the invention aims to solve]

[0004] In this industry, it is believed that doping modifications of the above-mentioned materials can solve existing problems. However, existing doping methods do not have a clear effect on improving charge / discharge voltage or the diffusion of active ions. [Means for solving the problem]

[0005] In view of this, the present disclosure provides a cathode active material. By doping the phosphorus site of an alkali metal vanadium phosphate with at least one of As, Sb, Bi, etc., the charge-discharge voltage and ionic conductivity of the material may be effectively improved.

[0006] Specifically, a positive electrode active material is provided in a first aspect of this disclosure. The general formula of the positive electrode active material is A3V 2-x M x (P 1-y E y The formula contains O4)3, where A represents an alkali metal element, M represents a doping element that substitutes for V, M includes one or more transition metal elements and rare earth elements, E represents a doping element that substitutes for P, E includes one or more of As, Sb, and Bi, and 0≦x≦1, 0 <y≦1 / 3である。

[0007] By doping with elements of the same group with ionic radii greater than P, the element P in the lattice of A3V2(PO4)3 can be appropriately replaced, which leads to an expansion of the unit cell. + Expand the ion transport channel, A + Reducing the energy barrier of ion transfer can improve the electronic conductivity of the material, which in turn can promote an improvement in the material's rate performance. Furthermore, doping phosphorus sites with element E can also improve the operating voltage of doped A3V2(PO4)3 materials, which contributes to an increase in energy density.

[0008] In one embodiment, M includes one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ti, Mo, Nb, Zr, La, and Ce.

[0009] In one embodiment, M includes one or more of Cr, Mn, Fe, and Ti.

[0010] In one embodiment, E is one or more of As and Bi.

[0011] In one embodiment, M is Fe and E is As.

[0012] In one embodiment, A contains one or more of Li, Na, and K.

[0013] In one embodiment, x is in the range of 0.001 ≦ x ≦ 1.

[0014] In one embodiment, x is in the range of 0.01 ≦ x ≦ 1.

[0015] In one embodiment, x is in the range of 0.3 ≦ x ≦ 0.5.

[0016] In one embodiment, y is in the range of 1 / 18 ≦ y ≦ 1 / 3.

[0017] In one embodiment, y is 1 / 6, 1 / 3, or 1 / 18.

[0018] In one embodiment, y is in the range of 1 / 18 ≦ y ≦ 1 / 6.

[0019] In one embodiment, y is in the range of 1 / 6 ≦ y ≦ 1 / 3. In a second aspect of the present disclosure, a method for manufacturing a positive electrode active material including the following steps is provided.

[0020] The positive electrode active material A3V to be manufactured 2-x M x (P 1-y E y Element sources of various elements of O4)3 are mixed to obtain a precursor material, where A represents an alkali metal element, M represents a doping element substituting for V, M includes one or more of a transition metal element and a rare earth element, E represents a doping element substituting for P, E includes one or more of As, Sb, and Bi, 0 ≦ x ≦ 1, 0 < y ≦ 1 / 3.

[0021] The precursor material is sintered to obtain a positive electrode active material.

[0022] The method for manufacturing positive electrode active material is simple in its manufacturing process, easy to operate, and therefore suitable for use in mass production.

[0023] In one embodiment, the precursor material is produced by the sol-gel method as follows: Source A, vanadium source, phosphorus source, M source, and E source are mixed in a solvent, and the resulting mixed solution is heated and stirred until the solvent evaporates to dryness to obtain the precursor material.

[0024] In one embodiment, the precursor material is produced by solid-phase ball milling as follows: Source A, vanadium source, phosphorus source, M source, and element E-containing doping anion source are ball-milled in the absence of a solvent to obtain the precursor material.

[0025] In one embodiment, sintering is carried out under an inert gas atmosphere, the sintering temperature is 400 to 900°C, and the sintering time is 10 to 30 hours.

[0026] In one embodiment, the inert gas includes one or more of nitrogen, argon, and helium.

[0027] A third aspect of this disclosure provides a positive electrode comprising a positive electrode active material provided in a first aspect of this disclosure. The positive electrode may be used to provide a battery having good rate performance and high energy density.

[0028] A fourth aspect of this disclosure provides a rechargeable battery, which includes a positive electrode provided in a third aspect of this disclosure.

[0029] A fifth aspect of this disclosure provides an electrical device, which includes a rechargeable battery, as provided in a fourth aspect of this disclosure. [Brief explanation of the drawing]

[0030] [Figure 1A] This figure shows the molecular structures of Na3V2(PO4)3(NVP) and its fully charged compound, NaV2(PO4)3. [Figure 1B] This figure shows the molecular structures of Na3V1.5Fe0.5(PO4)3(Fe-NVP) and its fully charged compound, NaV1.5Fe0.5(PO4)3. [Figure 1C] This figure shows the molecular structures of Na3V1.5Fe0.5(P17 / 18As1 / 18O4)3(As1-Fe-NVP) and its fully charged compound in Example 1. [Figure 1D] This figure shows the molecular structures of Na3V1.5Fe0.5(P5 / 6As1 / 6O4)3(As3-Fe-NVP) and its fully charged compound in Example 2. [Figure 1E] This figure shows the molecular structures of Na3V1.5Fe0.5(P2 / 3As1 / 3O4)3(As6-Fe-NVP) and its fully charged compound in Example 3. [Figure 2] This is a schematic flowchart of a method for producing a positive electrode active material according to embodiments of the present disclosure. [Figure 3] This is a summary of the X-ray diffraction (XRD) patterns of the positive electrode active materials provided in Examples 1-3 and Comparative Examples 1-2 of this disclosure. [Figure 4] This document summarizes the cycle performance curves at 0.5C for batteries manufactured using the positive electrode active materials provided in Examples 2, 4-5, and 10 of this disclosure, as well as for batteries manufactured using the material of Comparative Example 1. [Figure 5] This table summarizes the curves of specific discharge capacity versus cycle count at different rates for batteries manufactured using the positive electrode active materials provided in Examples 2, 4-5 and 10 of this disclosure, as well as for batteries manufactured using the material of Comparative Example 1. [Modes for carrying out the invention]

[0031] Sodium vanadium phosphate (Na3V2(PO4)3, NVP) is a common sodium superionic conductor (NASICON) cathode material. It has a stable crystal structure, good safety performance, and high theoretical specific capacity. However, it has low ionic and electronic conductivity, resulting in low rate performance, a low charge / discharge voltage plateau, and does not contribute to improving the energy density of sodium batteries.

[0032] In view of the issues associated with NVP, embodiments of this disclosure provide a positive electrode active material. The general formula of the positive electrode active material is A3V 2-x M x (P 1-y E y The formula contains O4)3, where A represents an alkali metal element, M represents a doping element that substitutes for V, M includes one or more transition metal elements and rare earth elements, E represents a doping element that substitutes for P, E includes one or more of As, Sb, and Bi, x represents the molar ratio in which element V is replaced by element M, y represents the molar ratio in which element P is replaced by element E, and 0≦x≦1, 0 <y≦1 / 3である。

[0033] Element E is an element of the same group as P, but with a larger ionic radius than P. E can be readily doped into the lattice of A3V2(PO4)3 and replace P at some positions, causing an expansion of the unit cell. This is because A + This expands the ion transport channel, reduces the energy barrier to movement, and reduces the repulsive effect of surrounding atoms, and therefore, A +This improves the ion migration speed and enhances rate performance. Furthermore, the crystal structure of the A3V2(PO4)3 material contains PO4 tetrahedra and VO6 octahedrons, which are connected at their vertices by shared oxygen (O) atoms. Doping the phosphorus site with element E alters the charge value of the surrounding O atoms, which forces a change in the charge environment around the V atoms, inducing element V to undergo redox reactions at a high potential. Thus, it improves the operating voltage of the doped A3V2(PO4)3 material and promotes an increase in the material's energy density. In addition, doping the phosphorus site with element E also reduces the band gap of the M-doped A3V2(PO4)3 material, attracting more electrons closer to the Fermi surface and improving the material's electronic conductivity. Moreover, the amount of element E doping is controlled not to be too high to ensure that the material has not only good structural stability but also good electronic conductivity, good ionic conductivity, and a high charge / discharge voltage plateau. Thus, the battery may be promoted to have good safety, good rate performance, and high energy density, etc.

[0034] Furthermore, in A3V2(PO4)3, if an appropriate amount of element E is used to dope the P site and an appropriate amount of metallic element M is used to dope the vanadium (V) site, the voltage plateau of the double-doped material will be greater than that of A3V2(PO4)3 doped only with E, due to the synergistic effect of doping element M to the V site and doping element E to the P site. 1-y E y A3V made of O4)3 material and doped only with element M. 2-x M x Compared to (PO4)3 material, further improvements are possible. The charge / discharge voltage plateau of the double-doped material is clearly improved, A + The energy barrier for ion transfer is clearly reduced.

[0035] In one embodiment of this disclosure, M may include one or more of chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), titanium (Ti), molybdenum (Mo), niobium (Nb), zirconium (Zr), lanthanum (La), and cerium (Ce). However, this disclosure is not limited to these.

[0036] In some embodiments of this disclosure, M includes one or more of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ti, Mo, Nb, and Zr. The cost of these elements is lower than that of the lanthanide elements La and Ce. The ionic radii of Ti, Mo, Nb, and Zr are larger than those of the V ion. The introduction of these doping elements also leads to an expansion of the lattice of A3V2(PO4)3, and therefore A + It promotes ion movement. However, the ionic radii of Cr, Mn, Fe, Co, Ni, Cu, and Zn are slightly smaller than the ionic radius of V ions. When these elements are simply doped into A3V2(PO4)3, the unit cell volume is reduced, but after the introduction of element E as described above, the unit cell volume is increased, promoting an improvement in the diffusion performance of the material. In some other embodiments of this disclosure, to better balance the cost of element M with its effect on the ionic conductivity and operating voltage of the material, element M can be one or more selected from Ti, Cr, Mn, and Fe. These elements also help to improve the operating voltage of the doped material and can be readily replaced with vanadium. Of these, Fe is the least expensive.

[0037] In one embodiment of this disclosure, E includes at least one of As, Sb, and Bi. The ionic radii of As, Sb, and Bi are all larger than the ionic radius of P. By doping these at the P site (i.e., replacing the position of the P atom in the crystal structure of A3V2(PO4)3 with an E atom), A3V 2-x M x (P 1-y E yThe volume of the O4)3 unit cell is moderately enlarged, which can reduce the energy barrier for A ion transfer. The ionic radii of As, Sb, and Bi are not excessively large compared to the ionic radius of P, which ensures that the material has not only higher stability of the crystal structure but also higher ionic conductivity. In some embodiments, element E is As and / or Bi. As and P are nonmetallic elements with similar properties, and As is more readily substituted for P.

[0038] In some embodiments, element M is Fe and element E is As. In this case, A3V 2-x M x (P 1-y E y O4)3 has a low manufacturing cost, P is replaced by As, which improves the migration rate of A ions, enhances the material's rate performance, and improves the operating voltage, thereby increasing the material's energy density.

[0039] In one embodiment of this disclosure, element A may specifically include one or more of Li, Na, K, etc. Element A can be selected depending on the specific type of secondary battery. For example, battery active material A3V 2-x M x (P 1-y E y When O4)3 is used in a sodium secondary battery, element A is Na.

[0040] In some embodiments of this disclosure, x is in the range of 0.001 ≤ x ≤ 1, and further in the range of 0.01 ≤ x ≤ 1. By controlling the doping amount of M within the above range, A3V caused by excessive doping of element M can be prevented. 2-x M x (P 1-y E yThe loss of electrochemical activity of O4)3 can be avoided, and the inability to improve electronic conductivity due to insufficient doping of element M can also be avoided. In some embodiments, s is in the range of 0.001 to 0.5, preferably 0.01 to 0.5, more preferably 0.1 to 0.5, and more preferably 0.3 to 0.5.

[0041] In some embodiments of this disclosure, y is in the range of 1 / 18 ≤ y ≤ 1 / 3. By controlling the doping amount of element E within the above range, A3V 2-x M x (P 1-y E y The unit cell volume of O4)3 is significantly increased without increasing the risk of structural collapse due to excessive changes in its crystal structure, and its ionic conductivity is improved. Thus, the material is guaranteed to have good cycling performance, the operating voltage of the material is significantly improved, the band gap of the material is extremely narrow, and therefore the conductivity is improved.

[0042] In some embodiments of this disclosure, y is 1 / 6. In this case, A3V 2-x M x (P 1-y E y In the O4)3 material, the energy barrier to A ion movement is extremely low, resulting in excellent rate performance and excellent cycle performance. In some other embodiments, y is 1 / 3. In this case, A3V 2-x M x (P 1-y E y The O4)3 material has the highest operating voltage and the best electronic conductivity. In some other embodiments, y is 1 / 18. In this case, A3V 2-x M x (P 1-y E y The O4)3 material has a very high degree of crystallinity and very good structural stability. In some embodiments, y is in the range of 1 / 18 ≤ y ≤ 1 / 6. In some other embodiments, y is in the range of 1 / 6 ≤ y ≤ 1 / 3.

[0043] In response to this, as shown in Figure 2, embodiments of the present disclosure provide a method for producing a positive electrode active material. Specifically, the method for producing a positive electrode active material includes the following steps:

[0044] 10: The positive electrode active material A3V to be manufactured. 2-x M x (P 1-y E y A precursor material is obtained by mixing various elemental sources of O4)3, where A represents an alkali metal element, M represents a doping element that substitutes for V, M includes one or more transition metal elements and rare earth elements, E represents a doping element that substitutes for P, E includes one or more of As, Sb, and Bi, and 0≦x≦1, 0 <y≦1 / 3である。

[0045] 20: The precursor material is sintered to obtain the positive electrode active material.

[0046] The method for manufacturing positive electrode active materials is suitable for mass production because the manufacturing process is simple and the operation is easy.

[0047] In step 10, the various element sources used to produce the positive electrode active material include an A source, a vanadium source, a phosphorus source, an M source containing a doping metal element M, and an E source containing a doping element E. The A source, vanadium source, M source, phosphorus source, and E source may be weighed according to the weight ratios of elements A, V, M, P, and E in the order 3:(2-x):x:(1-y):y. Furthermore, considering that alkali metal elements are prone to elemental loss in the subsequent sintering process, the A source may be in excess or in small amounts by 10%.

[0048] Source A may include one or more of the sodium source, lithium source, and potassium source, specifically one or more of alkali metal element nitrates, oxalates, acetates, acetylacetonates, carbonates, sulfates, phosphates, and hydroxides. The vanadium source may include one or more of the trivalent vanadium source, tetravalent vanadium source, and pentavalent vanadium source. Specifically, the vanadium source can be vanadium oxides (vanadium pentoxide, vanadium tetroxide, vanadium trioxide, etc.), hydroxides, metavanadates (ammonium metavanadate, sodium metavanadate, etc.), nitrates, sulfates, phosphates, oxalates, acetates, vanadium acetylacetonate, and vanadyl acetylacetonate. The M source containing the doping metal element M may be the same as the vanadium source described above, and may be one or more selected from oxides, hydroxides, nitrates, sulfates, phosphates, oxalates, acetates, and acetylacetonates of element M. The phosphorus source may be a polyanionic source of P, for example, an oxyacid source of P. In some embodiments, the phosphorus source is H3PO4, Na3PO4, and Li + kaNa + , K + NH4 + The phosphorus source may include one or more of dihydrogen phosphates, hydrogen phosphates, and orthophosphates. The E source may be one or more of oxides, acids, salts, etc., corresponding to As, Sb, and Bi. In some embodiments, the E source may be a doping anion source containing element E, such as one or more of oxyacids and oxysalts corresponding to As, Sb, and Bi. Of the element sources described above, the phosphorus source may be the same substance as the alkali metal source, vanadium source, or M source; for example, sodium phosphate can function as both a phosphorus source and a sodium source.

[0049] In this disclosure, the mixing method may be a liquid-phase method or a solid-phase method. The solid-phase method may be one or more of the following: mechanical stirring, ball milling, and mechanical fusion. The liquid-phase method may be a sol-gel method, a hydrothermal / solvothermal method, a liquid-phase high-energy ball milling method, and the like. The solvent used in the liquid-phase method may be one or more of the following: water, ethanol, and acetone.

[0050] In some embodiments, the precursor material is produced by solid-phase ball milling. Specifically, this process is as follows: an alkali metal source, a vanadium source, a phosphorus source, an M source, and an E-containing doped anion source are ball-milled in the absence of a solvent to obtain the precursor material.

[0051] In some other embodiments, the precursor material is produced by a sol-gel method. Specifically, this process is as follows: An alkali metal source, a vanadium source, and a phosphorus source are mixed in a solvent with a doping anion source containing an M source and element E. The resulting mixed solution is heated and stirred until the solvent evaporates to dryness to obtain the precursor material. During the heating and stirring process, various element sources react to obtain the precursor material. The precursor material may be converted into the cathode active material required after sintering. In one embodiment of this disclosure, the heating and stirring temperature can be 30 to 200°C, for example, 40 to 100°C, depending on the boiling point of the solvent used. The stirring speed during heating and stirring can be 300 to 900 rpm, and the time can be 1 to 6 hours.

[0052] In one embodiment of the present disclosure, sintering is carried out under an inert gas atmosphere, the sintering temperature is 400 to 900°C, and the sintering time is 10 to 30 hours. The inert gas may be one or more of nitrogen, argon, and helium, with argon and helium being preferred.

[0053] Embodiments of the present disclosure further provide a positive electrode comprising a positive electrode active material. The positive electrode may be used to manufacture a secondary battery having excellent performance, such as good rate performance and high energy density.

[0054] In one embodiment of the present disclosure, the positive electrode generally includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material. Furthermore, the positive electrode active material layer may also contain a binder and optionally a conductive agent. The binder and conductive agent can be conventional choices in the field of batteries.

[0055] The positive electrode current collector may include, but is not limited to, a variety of materials suitable for use as a positive electrode current collector, such as metal foil, alloy foil, metallized polymer film, or the aforementioned materials coated with carbon. The metal foil may be aluminum foil, the alloy foil may be aluminum alloy foil, and the metal plated on the surface of the polymer film may be an aluminum layer or an aluminum alloy layer.

[0056] Embodiments of the present disclosure further provide a secondary battery, the secondary battery including a positive electrode. The secondary battery may specifically be a lithium secondary battery, a sodium secondary battery, or a potassium secondary battery.

[0057] Because doped A3V2(PO4)3 is used as the positive electrode active material, the secondary battery has high energy density, good rate performance, and good cycle performance.

[0058] Embodiments of this disclosure further provide electronic devices. Electrical devices include rechargeable batteries. Electrical devices may be vehicles, ships, 3C products (including computers, communications, and home appliances), or energy storage systems.

[0059] Because the secondary battery uses doped A3V2(PO4)3 as the positive electrode active material, it has high energy density, good rate performance, and good cycle performance. When used in electrical equipment, the secondary battery can improve the performance and market competitiveness of the electrical equipment.

[0060] The secondary battery may be a liquid battery using a liquid electrolyte, or it may be a semi-solid battery or a solid battery using a semi-solid electrolyte or a solid electrolyte. In some embodiments, the secondary battery may include a positive electrode sheet, a negative electrode sheet, a separator and electrolyte disposed between the positive and negative electrode sheets. In some other embodiments, the secondary battery may include a positive electrode sheet, a negative electrode sheet, and a semi-solid or solid electrolyte disposed between the positive and negative electrode sheets. Furthermore, when a semi-solid or solid electrolyte is used, the positive and negative electrode sheets may also include a semi-solid electrolyte material or a solid electrolyte material.

[0061] The technical solutions of this disclosure will be described in more detail by examples. [Examples]

[0062] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 It contains O4)3(As1-Fe-NVP).

[0063] As1-Fe-NVP was manufactured as follows:

[0064] (1) According to the molar ratio of Na:V:Fe:P:As = 3:1.5:0.5:17 / 18:1 / 18, a sodium source (specifically sodium nitrate), a vanadium source (specifically vanadium pentoxide), an Fe source (specifically ferrous oxide), a phosphorus source (specifically phosphoric acid), and an As source (specifically ammonium arsenate) were weighed, mixed in the solvent ethanol, and heated at 80°C with stirring until the solvent evaporated to dryness to obtain the precursor material.

[0065] (2) The precursor material is sintered in a nitrogen atmosphere at a sintering temperature of 800°C for 12 hours, and Na3V 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 O4)3 was obtained. [Examples]

[0066] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 It contains O4)3(As3-Fe-NVP).

[0067] The method for producing As3-Fe-NVP was the same as in Example 1, except that the amounts of the P source and As source were changed so that the molar ratio of Fe:P:As was 0.5:5 / 6:1 / 6. [Examples]

[0068] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 2 / 3 As 1 / 3 It contains O4)3(As6-Fe-NVP).

[0069] The method for producing As6-Fe-NVP was the same as in Example 1, except that the amounts of the P source and As source were changed so that the molar ratio of Fe:P:As was 0.5:2 / 3:1 / 3.

[0070] Comparative Example 1 The positive electrode active material has the general formula Na3V2(PO4)3(NVP).

[0071] The method for producing NVP was the same as in Example 1, except that the As and Fe sources were not introduced.

[0072] Comparative Example 2 The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 It contains (PO4)3(Fe-NVP).

[0073] The method for producing Fe-NVP was the same as in Example 1, except that an As source was not introduced.

[0074] Figure 1A shows the molecular structures of Na3V2(PO4)3(NVP) and its fully charged compound NaV2(PO4)3. Figure 1B shows Na3V 1.5 Fe 0.5 (PO4)3(Fe-NVP) and its fully charged compound NaV 1.5 Fe 0.5 The molecular structure of (PO4)3 is shown. Figure 1C shows As1-Fe-NVP and its fully charged compound NaV in Example 1. 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 The molecular structure of O4)3 is shown.

[0075] In Figure 1A, in the Na3V2(PO4)3 unit cell, all 12 V atoms are at the centers of various VO6 octahedra, all 18 P atoms are at the centers of various PO4 tetrahedra, and 72 O atoms are used to connect the octahedra and tetrahedra to form the skeletal structure of the A3V2(PO4)3 compound. The remaining 18 Na atoms uniformly occupy the vacancies in the above skeletal structure. The unit cell described above has two types of Na sites in different oxygen environments: the 6b site at the center of the octahedra and the 18e site at the center of the tetrahedra, which are marked as Na1 sites and Na2 sites, respectively. In the Na3V2(PO4)3 unit cell, there are 6 Na atoms at the Na1 sites (indicated by dashed arrows) and 12 Na atoms at the Na2 sites. The sodium ions at the Na1 site are difficult to extract, and typically, the sodium ions at the Na2 site are deintercalated during the charge-discharge process, completing the transformation of the crystal structure between uncharged Na3V2(PO4)3 and fully charged NaV2(PO4)3. The six Na ions in the unit cell of fully charged NaV2(PO4)3 occupy the Na1 site.

[0076] In FIG. 1B, Fe-NVP may be regarded as having three Fe atoms uniformly substituted for three out of the twelve V atoms in the molecular structure of Na3V2(PO4)3 in FIG. 1A. The fully charged compound of Fe-NVP is NaV 1.5 Fe 0.5 (PO4)3, which has a structure different from that of Fe-NVP in that the Na atoms at the Na2 sites are removed.

[0077] In FIG. 1C, As1-Fe-NVP may be regarded as having one P atom out of the P atoms in the third layer replaced by one As atom (indicated by the solid line arrow) in the molecular structure of Fe-NVP in FIG. 1B. The fully charged compound of As1-Fe-NVP is NaV 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 O4)3, which has a structure different from that of As1-Fe-NVP in that the Na atoms at the Na2 positions are removed (the dotted line arrow indicates the Na atom at the Na1 position, and the remaining spherical atoms are Na2 atoms).

[0078] FIG. 1D shows the molecular structures of As3-Fe-NVP and its fully charged compound NaV 1.5 Fe3] 0.5 (P 5 / 6 As 1 / 6 O4)3 in Example 2. The molecular structure of As3-Fe-NVP is equivalent to that in which three out of the twelve V atoms in the molecular structure of NVP are equally replaced by three Fe atoms, and one P atom out of every other layer of the six layers of P atoms is replaced by an As atom, with a total replacement by three As atoms (indicated by the solid line arrow).

[0079] << [[ID= =32]]FIG. 1E shows the molecular structures of As6-Fe-NVP and its fully charged compound NaV 1.5 Fe 0.5 (P 2 / 3 As 1 / 3The molecular structure of O4)3 is shown. The molecular structure of As6-Fe-NVP is equivalent to the molecular structure of NVP in which 3 of the 12 V atoms are evenly replaced by 3 Fe atoms, and in each of the 6 layers of P atoms, 1 P atom is replaced by an As atom, for a total of 6 As atom replacements (shown by solid arrows).

[0080] Based on the molecular structures of the compounds shown in Figures 1A to 1E, the unit cell volume, the percentage change in unit cell volume in the uncharged state relative to the fully charged state (%), the open-circuit voltage, the band gap, and the energy barrier for sodium ion transfer of NVP, Fe-NVP, As1-Fe-NVP, As3-Fe-NVP, and As6-Fe-NVP can be determined according to the first-principles predictive method. The relevant results are summarized in Table 1 below.

[0081] The rate of change in the volume of a unit cell in an uncharged state relative to a fully charged state is explained using As1-Fe-NVP as an example. The rate of change in the volume of a unit cell in an uncharged state relative to a fully charged state is equivalent to that of a fully charged NaV 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 Unit cell volume of O4)3 and uncharged Na3V 1.5 Fe 0.5 (P 17 / 18 As 1 / 18 It is obtained by dividing the absolute difference from the unit cell volume of O4)3(As1-Fe-NVP) by the unit cell volume in the uncharged state. Uncharged compound A3V 2-x M x (P 1-y E y For the open-circuit voltage of O4)3, the lattice constants and total energy of the unit cell structure of the uncharged compound and the fully charged compound can be obtained from their respective molecular structures, and these can be used to determine A3V 2-x M x (P 1-y E yThe open-circuit voltage of O4)3 is calculated. The band gap may be calculated from the density of states distribution curve of the material. The energy barrier for Na ion movement may be calculated by the Nudged Elastic Band (NEB) method or the modified NEB method. [Table 1]

[0082] As can be seen from Table 1, when only Fe is doped into NVP, the unit cell volume is reduced because the atomic radius of Fe is smaller than that of V. When As is further doped into Fe-doped NVP, the unit cell volume increases with increasing As doping concentration, indicating that the introduction of As promotes unit cell expansion.

[0083] Doping with Fe alone and co-doping with Fe and As result in different changes in the unit cell volume of the uncharged state relative to the charged state of the material. As can be seen from Table 1, As3-Fe-NVP has the smallest change in unit cell volume of the uncharged state relative to the fully charged state and exhibits the highest crystal structure stability. Furthermore, although the unit cell volume change rates of Fe-NVP, As1-Fe-NVP, and As3-Fe-NVP in the uncharged state relative to the fully charged state are larger than those of NVP, their crystal structures are stable, ensuring that the structure does not collapse due to excessive deformation during the charge-discharge process.

[0084] As can be seen from Table 1, the open-circuit voltages of the Fe and As co-doped materials (Examples 1-3) are clearly improved compared to undoped NVP and Fe-NVP doped with iron alone. When this material is used in a sodium battery, the energy density of the battery is enhanced. Furthermore, with increasing As doping concentration, the open-circuit voltage of Fe and As co-doped NVP always increases, thus improving the energy density of the battery. Since the open-circuit voltage of a material is generally higher than its operating voltage, if the open-circuit voltage of material A is higher than the open-circuit voltage of material B, then the operating voltage of material A is generally higher than the operating voltage of material B. Therefore, the energy density of the manufactured battery may be estimated by comparing the open-circuit voltages of different materials.

[0085] As can be seen from Table 1, the band gap of each compound shows that undoped NVPs have a wider band gap and greater resistance. The band gap of Fe-NVP, doped with iron alone, can be reduced to 0.82 eV, and co-doping with Fe and As can further reduce the band gap. As3-Fe-NVP and As6-Fe-NVP show almost no band gap and high conductivity.

[0086] As can be seen from Table 1, the energy barrier for the movement of each compound is relatively high, at approximately 0.612 eV, for Na ion movement in NVP. The energy barrier for Na ion movement increases after the introduction of Fe doping alone. This is mainly because Fe has a small ionic radius, and doping with iron alone reduces the unit cell volume of NVP. In contrast, the energy barrier for Na ion movement in As1-Fe-NVP, As3-Fe-NVP, and As6-Fe-NVP, which are co-doped with Fe and As, is clearly reduced, improving ionic conductivity and thus increasing the charge-discharge rate of the material.

[0087] Furthermore, Figure 3 summarizes the measured XRE patterns for NVP, Fe-NVP, As1-Fe-NVP, As3-Fe-NVP, and As6-Fe-NVP. As can be seen from Figure 3, compared to the main diffraction peak in the XRE pattern of undoped NVP, after Fe doping, the position of the main peak is shifted slightly to the right, and the lattice parameters are generally highly consistent with NVP. Based on Fe doping, with As doping, at low concentrations (e.g., As1-Fe-NVP), the main peak shifts to the right, and as the doping concentration increases (e.g., As1-Fe-NVP), the full width at half maximum of some high-intensity peaks widens slightly, and the intensity of some low-intensity peaks also improves to varying degrees. This indicates that co-doping with Fe and As can change the crystal growth direction of NVP, enabling the growth of planes that were previously difficult to grow, and suggesting that co-doping with Fe and As can control the morphology and size of NVP. [Examples]

[0088] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 5 / 6 S 1 / 6 It has O4)3.

[0089] Na3V 1.5 Fe 0.5 (P 5 / 6 S 1 / 6 The manufacturing method for O4)3 is the same as that of Example 2, except that the As source is replaced with an Sb source (specifically sodium antimonate). 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0090] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 5 / 6 Bi 1 / 6 It has O4)3.

[0091] Na3V 1.5 Fe 0.5 (P 5 / 6 Bi 1 / 6 The method for producing O4)3 is the same as in Example 2, except that the As source is replaced with a Bi source (specifically, bismuth ammonium citrate). 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0092] The positive electrode active material has the general formula Na3V 1.8 Fe 0.2 (P 5 / 6 As 1 / 6 It has O4)3.

[0093] Na3V 1.8 Fe 0.2 (P 5 / 6 As 1 / 6 The manufacturing method for O4)3 is the same as that of Na3V in Example 2, except that the amounts of Fe and V sources were changed so that the molar ratio of V element to Fe element was 1.8:0.2. 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0094] The positive electrode active material has the general formula Na3V 1.99 Fe 0.01 (P 5 / 6 As 1 / 6 It has O4)3.

[0095] Na3V 1.99 Fe 0.01 (P 5 / 6 As 1 / 6 The manufacturing method for O4)3 is the same as in Example 2, except that the amounts of the Fe source and V source were changed so that the molar ratio of element V to element Fe was 1.99:0.01. 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0096] The positive electrode active material has the general formula Na3V 1.5 Ti 0.5 (P 5 / 6 As 1 / 6 It has O4)3.

[0097] Na3V 1.5 Ti 0.5 (P 5 / 6 As 1 / 6 The manufacturing method for O4)3 is the same as that of Na3V in Example 2, except that the Fe source is replaced with a Ti source (specifically titania). 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0098] The positive electrode active material has the general formula Na3V 1.5 Cr 0.5 (P 5 / 6 As 1 / 6 It has O4)3.

[0099] Na3V 1.5 Cr 0.5 (P 5 / 6 As 1 / 6 The manufacturing method for O4)3 is the same as that of Na3V in Example 2, except that the Fe source is replaced with a Cr source (specifically, chromium oxide). 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0100] The positive electrode active material has the general formula Na3V 1.5 Nb 0.5 (P 5 / 6 As 1 / 6 It has O4)3.

[0101] Na3V 1.5 Nb 0.5 (P 5 / 6 As1 / 6 The manufacturing method for O4)3 is the same as that of Na3V in Example 2, except that the Fe source is replaced with an Nb source (specifically sodium niobate). 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0102] The positive electrode active material has the general formula Na3V2(P 17 / 18 As 1 / 18 It has O4)3.

[0103] Na3V2(P 17 / 18 As 1 / 18 The manufacturing method for O4)3 was the same as that of Example 1, except that a doping source - Fe source - was not used. [Examples]

[0104] The positive electrode active material has the general formula Na3V2(P 5 / 6 As 1 / 6 It has O4)3.

[0105] Na3V2(P 5 / 6 As 1 / 6 The manufacturing method for O4)3 was the same as that of Example 2, except that a doping source - Fe source - was not used. [Examples]

[0106] The positive electrode active material has the general formula Na3V2(P 2 / 3 As 1 / 3 It has O4)3.

[0107] Na3V2(P 2 / 3 As 1 / 3 The manufacturing method for O4)3 was the same as that of Example 3, except that a doping source - Fe source - was not used. [Examples]

[0108] The positive electrode active material has the general formula Na3VFe(P 5 / 6 As1 / 6 It has O4)3.

[0109] Na3VFe(P 5 / 6 As 1 / 6 The manufacturing method for O4)3 is the same as that of Na3V in Example 2, except that the amounts of the Fe source and V source were changed so that the molar ratio of element V to element Fe was 1:1. 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0110] The positive electrode active material has the general formula Na3V 1.5 Fe 0.5 (P 35 / 36 As 1 / 36 It contains O4)3. The manufacturing method is the same as in Example 2, except that the amounts of the P source and As source were changed so that the molar ratio of Fe:P:As element was 0.5:35 / 36:1 / 36. 1.5 Fe 0.5 (P 5 / 6 As 1 / 6 The manufacturing method was the same as that for O4)3. [Examples]

[0111] The positive electrode active material has the general formula Na3V 1.5 Mn 0.5 (P 5 / 6 As 1 / 6 It has O4)3. [Examples]

[0112] The positive electrode active material has the general formula Na3V 1.5 Mn 0.5 (P 5 / 6 Bi 1 / 6 It has O4)3. [Examples]

[0113] The positive electrode active material has the general formula Na3V1Mn1(P 5 / 6 Bi 1 / 6 It has O4)3. [Examples]

[0114] The positive electrode active material has the general formula Na3V 1.5 Mn 0.5 (P 5 / 6 S 1 / 6 It has O4)3. [Examples]

[0115] The positive electrode active material has the general formula Na3V 1.5 Ti 0.5 (P 5 / 6 Bi 1 / 6 It has O4)3.

[0116] Table 2 below summarizes the relevant electrochemical properties of the positive electrode active materials in Examples 4 to 20. [Table 2]

[0117] As can be seen from Table 2, compared to the undoped Na3V2(PO4)3 in Example 1, the double-doped vanadium sodium phosphate materials provided in Examples 4-10 and 14-20 of this disclosure can not only maintain good structural stability but also have a high open-circuit voltage, a narrow band gap, and a low energy barrier to Na ion movement, thus resulting in high energy density and good rate performance. Furthermore, by comparing Examples 11-13 in Table 1 with Examples 1-3, it can be seen that when Na3V2(PO4)3 is doped with the same amount of As without iron, the resulting material has a larger unit cell volume, a smaller rate of change in unit cell volume in the fully charged state compared to the uncharged state, and a reduced energy barrier to sodium ion movement. As a result, the rate performance of the battery is improved, but the open-circuit voltage and conductivity of the material are slightly reduced. Furthermore, when Na3V2(PO4)3 is doped with the same amount of As, Sb, or Bi, the open-circuit voltage of the material may be further improved after Mn is doped at the V site.

[0118] To further support the beneficial effects of the embodiments of this disclosure, the materials of the above-described examples and comparative examples were fabricated into batteries and their electrochemical performance was tested. The relevant results are shown in Table 3.

[0119] The battery manufacturing process was as follows: (1) Preparation of positive electrode sheet: The positive electrode active material of each example or comparative example, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVEF) were added to the solvent NMP (N-methylpyrrolidone) in a weight ratio of 88:6:6 and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector, which was aluminum foil, and then dried, rolled, and cut to obtain a positive electrode sheet. (2) Preparation of negative electrode sheet: The negative electrode active material (specifically hard carbon) and the binder (specifically styrene-butadiene rubber (SBR) and carboxymethyl cellulose sodium (CMC-Na) in a weight ratio of 2:3) were mixed with ionized water in a weight ratio of 95:5 and mixed until uniform to obtain a negative electrode slurry. The negative electrode slurry was coated onto a negative electrode current collector, which was copper foil, and then dried, rolled, and cut to obtain a negative electrode sheet. (3) Battery assembly: The positive electrode sheet, separator, and negative electrode sheet were sequentially stacked to obtain a dry cell. This dry cell was rolled up, placed in an aluminum-plastic film which served as the outer foil, and the electrolyte was poured in. After processes such as vacuum packaging, settling, chemical formation, and molding, the manufacture of the sodium whole cell was completed.

[0120] The batteries of each example and comparative example were tested for the following electrochemical properties.

[0121] 1) Cycle Performance: Each battery was subjected to charge-discharge cycle testing at 25°C at a rate of 0.5C. The voltage range was 2.5 to 4.3V. During charging, the battery was charged with a constant current of 0.5C until the cutoff voltage reached 4.3V, and then charged with a constant voltage until the cutoff current reached 0.05C. During discharging, the battery was discharged to 2.5V with a constant current of 0.5C. The discharge capacity per gram in the first cycle and the capacity retention rate after 50 cycles were recorded for each battery. The discharge capacity per gram in the first cycle is equal to the ratio of the discharge capacity in the first cycle of each sodium whole battery to the weight of the positive electrode active material in the battery. The capacity retention rate after 50 cycles is equal to the ratio of the discharge capacity after 50 cycles to the discharge capacity in the first cycle.

[0122] Furthermore, the discharge curve obtained from the charge-discharge curves at constant current charge-discharge at 0.5C for each battery was integrated and divided by the discharge capacity to determine the average voltage of each battery. The relevant results are summarized in Table 3 below, and the cycle curves of some examples and comparative examples are summarized in Figure 4.

[0123] 2) Rate Performance: The change in discharge capacity per gram over cycles for each battery at 0.5C, 1C, 5C, and 10C was tested at 25°C. The voltage range was 2.5 to 4.3V. Rate performance curves for some examples and comparative examples are shown in Figure 5. When calculating the discharge capacity per gram, the ratio of the discharge capacity at a given current density to the weight of the positive electrode active material was considered to be the discharge capacity per gram at that current density. Table 3 summarizes the discharge capacity per gram in the first cycle at the 10C rate for each battery, and the ratio of the discharge capacity in the first cycle at the 10C rate to the discharge capacity in the first cycle at the 0.5C rate. [Table 3]

[0124] As can be seen from Table 3, compared to the sodium battery manufactured with the material of Comparative Example 1, the sodium batteries manufactured with the materials provided in Examples 1 to 20 of this disclosure have a higher voltage plateau and a higher first-cycle discharge capacity ratio at 10C / 0.5C, demonstrating higher battery rate performance. Furthermore, the battery cycle performance is not significantly reduced. In addition, the batteries of Examples 1 to 7 and 14 to 15 have a higher voltage plateau and better rate performance than the battery of Comparative Example 2.

[0125] Exemplary embodiments of the present disclosure have been described above. It should be noted that several improvements and modifications can be made by those skilled in the art without departing from the principles of the present disclosure, and these will fall within the scope of the present disclosure.

Claims

1. A positive electrode active material wherein the positive electrode active material is of general formula A ３ V ２－ｘ M ｘ (P １－ｙ E ｙ O ４ ) ３ A positive electrode active material comprising the formula, wherein A represents an alkali metal element, A comprises Na, M represents a doping element that substitutes V, M comprises one or more of Cr, Mn, Fe, Ti, and Nb, E represents a doping element that substitutes P, E comprises one or more of As, Sb, and Bi, and 0 ≤ x ≤ 1 and 0 < y ≤ 1 / 3.

2. The positive electrode active material according to claim 1, wherein M comprises one or more of Cr, Mn, Fe, and Ti.

3. The positive electrode active material according to claim 1 or 2, wherein E is one or more of As and Bi.

4. The positive electrode active material according to claim 1, wherein M is Fe and E is As.

5. The positive electrode active material according to any one of claims 1, 2, and 4, wherein x is in the range of 0.001 ≤ x ≤ 1.

6. The positive electrode active material according to any one of claims 1, 2, and 4, wherein x is in the range of 0.01 ≤ x ≤ 1.

7. The positive electrode active material according to any one of claims 1, 2, and 4, wherein x is in the range of 0.3 ≤ x ≤ 0.

5.

8. The positive electrode active material according to any one of claims 1, 2, and 4, wherein y is in the range of 1 / 18 ≤ y ≤ 1 / 3.

9. The positive electrode active material according to any one of claims 1, 2, and 4, wherein y is 1 / 6, 1 / 3, or 1 / 18.

10. The positive electrode active material according to any one of claims 1, 2, and 4, wherein y is in the range of 1 / 18 ≤ y ≤ 1 / 6.

11. The positive electrode active material according to any one of claims 1, 2, and 4, wherein y is in the range of 1 / 6 ≤ y ≤ 1 / 3.

12. A method for manufacturing a positive electrode active material, The positive electrode active material A to be manufactured ３ V ２－ｘ M ｘ (P １－ｙ E ｙ O ４ ) ３ Mixing element sources of various elements of to obtain a precursor material (10), where A represents an alkali metal element, A includes Na, M represents a doping element substituting for V, M includes one or more of Cr, Mn, Fe, Ti, and Nb, E represents a doping element substituting for P, E includes one or more of As, Sb, and Bi, 0 ≦ x ≦ 1, 0 < y ≦ 1 / 3, the step of mixing element sources to obtain a precursor material; The steps include: sintering the precursor material to obtain the positive electrode active material (20); A method that includes [something].

13. The manufacturing method according to claim 12, wherein the precursor material is produced by a sol-gel method comprising mixing source A, vanadium source, phosphorus source, M source, and E source in a solvent, and heating and stirring the resulting mixed solution until the solvent evaporates to dryness.

14. The manufacturing method according to claim 12, wherein the precursor material is produced by solid-phase ball milling, which comprises ball milling an A source, a vanadium source, a phosphorus source, an M source, and an E element-containing doping anion source in the absence of a solvent, to obtain the precursor material.

15. The manufacturing method according to any one of claims 12 to 14, wherein the sintering is carried out in an inert gas atmosphere, the sintering temperature is 400 to 900°C, and the sintering time is 10 to 30 hours.

16. A positive electrode comprising the positive electrode active material according to any one of claims 1, 2, and 4.

17. A secondary battery comprising the positive electrode described in claim 16.

18. An electrical device comprising a secondary battery as described in claim 17.

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